A New Global Theory of the Earth's Dynamics : a Single Cause Can Explain All the Geophysical and Geological Phenomena André Rousseau CNRS (UMS 2567) Université Bordeaux 1, Groupe d'Etude des Ondes en Géosciences 351 cours de la Libération, F-33405 Talence cedex [email protected] After describing all the contradictions associated with the current Plate Tectonics theory, this paper proposes a model where a single cause can explain all geophysical and geological phenomena. The source of the Earth's activity lies in the difference of the angular velocities of the mantle and of the solid inner core. The friction between both spheres infers heat, which is the cause of the melted iron which constitutes most of the liquid outer core, as well as the source of the global heat flow. The solid inner core angular velocity is supposed to remain steady, while the mantle angular velocity depends on gyroscopic forces (involving acceleration) and slowing down due to external attractions and, principally the motions of mantle plates 2900 km thick. The variations of the geomagnetic field are therefore the direct consequence of the variations of the angular velocity of the mantle relative to that of the inner core. As a result, the biological and tectonic evolutions during geological times are due to those phenomena. So, the limits of eras coincide exactly with the passage to zero of the geomagnetic field. Here we show that cycles of about 230-250 millions years, which exhibit the correlation between the mantle angular velocity variations, the geomagnetic variations, and therefore the climate, allow us to predict future events : the current global warming which parallels the Earth's magnetic field decrease, and the spoliation of the forests which are not damaged by acid rains, but in reality from their roots by acid liquid arising inside the cracks of the crust. 2 Finally, this geodynamics allows us to determine the mechanisms of earthquakes. Keywords Geodynamics, geomagnetism, orogeneses, core, mantle, thermoelectricity Since the discovery of the mid-oceanic ridges in the 1960's the continental drift model, proposed by Wegener in the 1930's and rejected at that time by the geoscientists, has been transformed into "Global Plate Tectonics" with the mechanical support of convection currents inside the mantle. But the continuing impossibility of predicting earthquakes reveals an insufficient knowledge of Earth's geodynamics, which can be compared to the state of knowledge in medicine before Pasteur's discovery of micro-organisms. As a confirmation of this comparison, Plate Tectonics must be continuously modified in order to "explain" an earthquake occurring in an unexpected area (such as the last Kobe earthquake, for example). This reminds one of the medieval period when the anti-Copernic astronomers had to invent the concept of epiglyptical movements of the planets in order to adjust the observations to the geocentric model of the Universe. That is why it would be wise to consider inadequate the empirical approach to the lithospheric plates defined by some statistical outlines of earthquake epicentres. Besides, in spite of the public success of Plate Tectonics theory, some authors, as A.A. Meyerhoff, pointed out the contradictions with reality and proposed a new global geodynamics, the Surge Tectonics (see Meyerhoff et al. (1996)), based on magmatic activity through the lithosphere, from the asthenosphere inside the upper mantle. Consequently, attempting to invent a possible mechanical model of the Earth's geodynamics, after abstracting from observed effects, may be fruitful if the consequences of this model fit the observed reality. If only one cause can explain the majority of the observations, which this paper intends to demonstrate, the probability that the theory is grounded in reality is great. 3 A.A. Meyerhoff located the "engine" of the Earth's dynamics at the bottom of the upper mantle. The model developed here "puts" it deeper, in the liquid outer core, which may be seen as a kind of magma. This model is based on the hypothesis of differences in the angular velocities of the solid inner core and of the mantle for mechanical reasons. This difference has already tentatively been put forward by several authors (Song and Richards, 1996 ; Su et al., 1996 ; Glatzmaier and Roberts, 1996 ; Jeanloz and Romanowicz, 1997 ; Aurnou et al., 1998). We intend to demonstrate that, in fact, such a phenomenon is essential. The heat emitted by the resulting friction causes the melting of the outer core, geothermal effect, and hot spots. The differences between the tangential velocities at the equator and at the poles of the surface of the inner core and of the periphery of the outer core infer a maximum friction at the equator tending to zero at the poles, and as a result producing a decreasing heat gradient. Consequently two electric fields originate for thermo electrical reasons from these two shells, which may be the source of the geomagnetism and explain its variations. However, magneto- hydro dynamics effect could also be a source of the geomagnetism under specific conditions. The concept of lithospheric plates 100 km thick is replaced by mantle plates 2900 km thick. From the variations of the geomagnetic field due to the variations in the angular velocity of the mantle, we show the consequences on climate and species during the geological times. The main orogeneses and glaciations periods are connected to the Earth's magnetism and prove to be integrated in a regular time cycle. Moreover earthquakes are not only caused by a plate confrontation. We present a calculation related to the magnetic field of the model, which makes it plausible. Assuming steady the present decrease of the Earth's angular velocity, which we only attribute to the mantle, we calculate the probable constant inner core angular velocity, and the electric charges responsible of the Earth's magnetism. Major problems of the current Plate Tectonics theory Following are the principle failings of the current Plate Tectonics theory. 1) The basic concept which supports the current Plate Tectonics theory is the assumption of convection movements located inside the mantle and caused by the heat of the core. There is however 4 a contradiction in the fact that the mantle lets shear waves propagate inside it, which reveal a crystalline structure inconsistent with the possibility of convection motions inside fluids. 2) The oceanic bottoms are flat and the sediments are not folded. We should take into account the pressure and constraints that the up-lifting and superficial parts of those convection currents would apply on the thin lithospheric Plates which are 100 kilometres thick and several thousands kilometres long ; it is not conceivable that these plates can exist without being at least crumpled. 3) The Benioff or "subduction" planes along which there would be the lithospheric slabs entering the mantle are said to be the location of earthquakes and active volcanoes : the evoked cause would be the mechanical effect and the heating due to the friction created by the downward slab. But there is inconsistency between mechanical ruptures (such as earthquakes) and melted rocks (such as magmas). Besides, the supposed mantle local magmatic zones ought to be cooled down by the cold elements introduced by downward slabs, which come from the surface, unless there are already melted zones extending round about at the depth of 100 kilometres. But it is unlikely, otherwise this would have been revealed by the lack of shear waves - nevertheless present -, as in the case of the fluid characteristics of the outer core. In addition, such a model does not explain the characteristic shape of island arcs. 4) The geothermal flux is reputed to be same all over the globe, and to be the consequence of the radioactive activity of the uranium present in crystalline rocks ; however, those rocks do not exist in the oceans (2/3 of the Earth's surface). 5) The inner core is solid and the outer core liquid ; as both parts are reputed to have the same composition, the opposite would be more logical given a central heat source. If the very high pressure was the cause of this state of fact, we could not have the existing sharp seismic interface between the outer and inner core. 6) One of the most upsetting enigmas is what occurs when the Earth's magnetic field is equal to zero, particularly in relation to the magnetosphere and the solar flux. One cannot be content with estimating this period too short to involve some consequences linked to the quantity of the solar flux hitting then the Earth's surface. The number of magnetic inversions should be examined primaruly from the volcanic samples, and not from the oceanic surface "inversions", the origin of which is not assured. 5 The oceanic bottoms are indeed more complicated than the descriptions made in accordance with the "canons" of Plate tectonics. So, Cretaceous sediments (instead of Miocene or later) and even sericitic carbonaceous phyllites and microquartzites, as well as carbonaceous shales were dredged in the equatorial segment of the mid-Atlantic ridge, where the investigation of the igneous rocks reveals a continental crustal relict of pre-Cretaceous or pre-Jurassic age (Udintsev et al., 1992 ; Udintsev and Kurentsova, 1993). Thus, it is difficult to attribute the variations of the oceanic magnetic field to the differences in the paleomagnetic directions of oceanic bed rock ; they are more probably due to the contact between paramagnetic peridotites and magnetic serpentinites (altered peridotites). 7) Finally, the cause of earthquakes occurring inside Plates which are supposedly impossible to distort should not be that of rubbing Plates. A new Geodynamic Model for the Earth Let us imagine the evolution of a very young spherical terrestrial planet of 6370 kilometres in radius, moved by its initial angular movement.